1. Field of the Invention
The invention relates to induction machine bearing systems, and more particularly to electric motor bearing systems including an active magnetic bearing and an auxiliary mechanical bearing, both supporting a rotatable shaft.
2. Description of the Prior Art
Induction machines, such as alternating current (AC) electric motors incorporate rotating shafts supported by bearings. Traditionally, motor bearings have included mechanical hydrostatic and hydrodynamic fluid film bearings and rolling element bearings.
In the more recent past, some induction machines have incorporated contactless magnetic bearings. An exemplary magnetic bearing is shown in U.S. Pat. No. 6,777,841. As is known in the art, magnetic bearings enable higher rotational speeds above traditional 50/60 Hz excitation frequencies, higher torque outputs and active shaft vibration damping: thereby enabling direct drive of compressors and other driven devices without the need for intermediate gear boxes that would otherwise provide variable speed or torque multiplication. It is desirable to dissipate heat generated within the region of the magnetic bearing (by the bearing itself or by the rest of the induction machine).
When magnetic bearings are employed in an induction machine, an auxiliary mechanical bearing system would be desirable in order to protect the magnetic bearing and the rest of the induction machine system in the event of magnetic bearing system failure or power failure. When such a failure occurs, the parallel mounted auxiliary bearings are intended to permit safe rundown of the induction machine equipment and reduce likelihood of damage to either the magnetic bearing or other machine structure. Upon magnetic bearing operational failure, motor shaft mechanical forces are transferred rapidly to the auxiliary bearing structure, causing potential impact shock to the magnetic bearing support structure as well as the auxiliary bearing. It is desirable to minimize potential damage to the induction machine that might be caused by such impact shock.
Mechanical bearings, including auxiliary bearings, often are serviced in accordance with a plant maintenance protocol. It is desirable to be able to service auxiliary bearings in as simple a fashion as is possible, with minimal time and effort.
Thus, a need exists in the art for an induction machine bearing system employing magnetic bearings that provides for: auxiliary bearings; bearing heat dissipation; reduction of potential impact shock to the magnetic bearing structure upon magnetic bearing failure; and ease of auxiliary bearing servicing.